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Linux pstree shows running processes as a tree. The tree is rooted at either pid or init if pid is omitted. If a user name is specified, all process trees rooted at processes owned by that user are shown.
Install pstree

#On Mac OS
brew install pstree
 
#On Fedora/Red Hat/CentOS
yum install psmisc #using psmisc package for pstree
 
#On Ubuntu/Debian APT
apt-get install psmisc
After above opeation, we can use

# man pstree | less

to check whether the installation is successful.